Oral glucose tolerance test

An oral glucose tolerance test measures the body's ability to use glucose, a type of sugar found in fruits and many other foods. (Glucose is the main source of energy used by the body.) After not eating all night, the person being tested drinks a special sugar solution on the morning of the test.

A blood sugar sample is taken from a vein in the person's arm once each hour for 3 hours to see how much the blood sugar increases and then decreases over time. The test is done in a doctor's office or lab.

The oral glucose tolerance test can be used to diagnose prediabetes and diabetes. It is commonly used to screen for or diagnose diabetes that develops during pregnancy (gestational diabetes). The oral glucose tolerance test for gestational diabetes may be slightly different from the test for prediabetes and diabetes.

The oral glucose tolerance test for type 2 diabetes is used less often than other blood sugar tests for type 2 diabetes because it costs more and requires several blood samples.